Thumb-activated adjustment lever



FIG. 1 is a perspective view of a thumb-activated adjustment lever showing our new design, associated adjustable structure being indicated in broken line;

FIG. 2 is a right hand end view of the lever thereof;

FIG. 3 is a left hand end view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a rear view thereof of a thumb-activated adjustment lever.

The broken lines are shown for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a thumb-activated adjustment lever, as shown and described. 